1. Field of the Invention
This invention relates generally to magnetic-recording media, and relates more particularly to a vertical-magnetic-recording disk having a high-permeability layer (preferably iron oxide) and a permanent-magnet ferrimagnetic layer (preferably barium ferrite) on a titanium alloy or austenitic stainless steel substrate.
2. Description of the Relevant Art
The preparation by sputtering of barium ferrite films without and with an underlying iron oxide film for the application of vertical-magnetic-recording disks has been carried out by M. Naoe and coworkers at Tokyo Institute of Technology, Tokyo Institute of Polytechnics, and Shinshu University in Japan. This work has been described in a series of technical papers as follows: M. Naoe, S. Hasunuma, Y. Hoshi, and S. Yamanaka, IEEE Trans. Magn. MAG-17, 3184 (1981); M. Matsuoka, Y. Hoshi, M. Naoe, and S. Yamanaka, IEEE Trans. Magn. MAG-18, 1119 (1982); M. Matsuoka, Y. Hoshi, M. Naoe, and S. Yamanaka, IEEE Trans. Magn. MAG-20, 800 (1984); A. Morisako and M. Matsumoto, IEEE Transl. J. Magn. Japan TJMJ-1, 39 (1985); Y. Matsuda, M. Matsuoka, M. Naoe, and Y. Hoshi, IEEE Transl. J. Magn. Japan TJMJ-1, 41 (1985); M. Matsuoka, M. Naoe, and Y. Hoshi, IEEE Transl. J. Magn. Japan TJMJ-1, 44 (1985); M. Matsuoka, M. Naoe, and Y. Hoshi, J. Appl. Phys. 57, 4040 (1985); M. Matsuoka, M. Naoe, and Y. Hoshi, IEEE Trans. Magn. MAG-21, 1474 (1985); A. Morisako, M. Matsumoto, and M. Naoe, J. Magn. Magn. Mater. 54-57, 1657 (1986); A. Morisako, M. Matsumoto, and M. Naoe, IEEE Trans. Magn. MAG-22, 1146 (1986); A. Morisako, M. Matsumoto, and M. Naoe, IEEE Trans. Magn. MAG-23, 56 (1987); A. Morisako, M. Matsumoto, and M. Naoe, IEEE Trans. Nagn. MAG-23, 2359 (1987); A. Morisako, M. Matsumoto, and N. Naoe, IEEE Trans. Magn. MAG-24, 3024 (1988); A. Morisako, M. Matsumoto, and M. Naoe, J. Magn. Soc. Japan 15, 401 (1991); A. Morisako, H. Nakanishi, M. Matsumoto, and M. Naoe, J. Appl. Phys. 75, 5969 (1994); A. Morisako, M. Matsumoto, and M. Naoe, J. Appl. Phys. 79, 4881 (1996). Also of note is A. Morisako, M. Matsumoto, and T. Yamasaki, J. Magn. Soc. Japan 22, 194 (1998), which pertains to the preparation of sputter-deposited strontium ferrite (SrFe.sub.12 O.sub.19) films for vertical magnetic recording.
In the first of the above-listed references, the substrate material is silica [silicon dioxide (SiO.sub.2)] glass (commonly called fused quartz). In the second reference, not only is this substrate material used, but also others: (1) single-crystal silicon (Si) wafer with (100) orientation, (2) thermally oxidized single-crystal silicon (Si) wafer [with (100) orientation] by which an outer conversion layer of silica (SiO.sub.2) glass is formed, and (3) single-crystal sapphire [aluminum oxide (Al.sub.2 O.sub.3)] with (102) orientation. In all the remaining references, only thermally oxidized single-crystal silicon wafers are used as the substrate material. The fourth and eighth references give the thickness of the thermally oxidized layer of silica (SiO.sub.2) glass as 5000 .ANG. (or 500 nm=0.5 .mu.m) on the single-crystal silicon (Si) wafer.
These materials are not practical for disk substrates in magnetic-recording applications because of their fragility and very expensive fabrication.
Furthermore, aluminum oxide (Al.sub.2 O.sub.3), as single-crystal sapphire or alumina ceramic, and silicon dioxide (SiO.sub.2), as silica glass or single-crystal quartz, are excellent electrical insulators. In disk-coating sputtering systems designed for fabricating magnetic-recording media, in which deposition takes places on both disk sides simultaneously, electrical-insulating disk substrates cannot be bias sputtered during deposition. Substrate bias sputtering is a convenient and powerful technique for controlling film morphology, but its use is precluded with electrical-insulating disk substrates in these systems.
D. E. Speliotis, Advanced Development Corp. (Burlington, Mass.), in 1990 proposed the use of silicon carbide ceramic as a material for disk substrates with sputtered vertical-magnetic-recording media of barium ferrite. Since that time, several people in the magnetic-recording industry have adopted this proposal, but have not yet produced any results. Pure silicon carbide (SiC) is an electrical insulator. However, with appropriate doping semiconductor behavior is obtained and the electrical resistivity can vary over a range of seven orders of magnitude.
In the period over 1987-1991, D. E. Speliotis and coworkers investigated and reported the magnetic-recording performance of media comprised of powder dispersions of barium ferrite crystallite platelet particulates in polymer plastic binders (so-called particulate media). The references are as follows: D. E. Speliotis, J. Appl. Phys. 61, 3878 (1987); D. E. Speliotis, IEEE Trans. Magn. MAG-23, 3143 (1987); D. E. Speliotis, J. Appl. Phys. 63, 3429 (1988); D. E. Speliotis, J. Appl. Phys. 63, 3432 (1988); D. E. Speliotis, IEEE Trans. Magn. MAG-24, 2850 (1988); D. E. Speliotis, IEEE Trans. Magn. MAG-25, 4048 (1989); D. E. Speliotis, J. Magn. Soc. Japan 13(S1), 351 (1989); D. E. Speliotis, J. Magn. Soc. Japan 13(S1), 887 (1989); D. E. Speliotis, IEEE Trans. Magn. MAG-26, 124 (1990); D. E. Speliotis, IEEE Trans. Magn. MAG-26, 141 (1990); D. E. Speliotis, J. Magn. Magn. Mater. 83, 455 (1990); D. E. Speliotis, IEEE Trans. Magn. MAG-26, 1891 (1990); M. Tsutsumi, F. Kugiya, N. Kodama, M. Suzuki, M. Koizumi, F. Akagi, and D. E. Speliotis, J. Appl. Phys. 69, 4493 (1991); and D. E. Speliotis and W. Lynch, J. Appl. Phys. 69, 4496 (1991).
D. E. Speliotis is among the investigators in a technical paper describing the sputtering of barium ferrite films deposited on several different kinds of substrates: (1) thermally oxidized single-crystal silicon (Si) wafers by which an outer conversion layer of silica (SiO.sub.2) glass is formed, (2) microcrystalline (vitreous) carbon (a-C), (3) high-radiofrequency-sputtered coating of amorphous silicon nitride (Si.sub.3 N.sub.4) on vitreous carbon, and (4) high-radiofrequency-sputtered coating of amorphous silicon dioxide (SiO.sub.2) on vitreous carbon. The reference is as follows: K. Sin, J. M. Sivertsen, J. H. Judy, Y. Hoshi, and D. E. Speliotis, J. Appl. Phys. 73, 6689 (1993).
The additional materials described above for disk substrates are, too, not practical because of their fragility and very expensive fabrication.